42 
Some Aspects of the Algce. 
water, while many of the filamentous forms (though apparently none of 
the isogamous ones) live both in the sea and also in freshwater. 
Practically all the Siphoneae are marine, and nearly all the Florideae 
and Phaeophyceae (mostly stenohaline forms). The exceptions 
among these latter groups may have wandered up through the 
brackish waters of river mouths to the mountain streams they 
mostly inhabit, or they may be the more resistant remnants of a 
marine flora in areas formerly covered by the sea. 
The remaining sections of this chapter deal with Temperature 
and Light. The latter is, of course, the more important as an 
ecological factor, though the relations of the different algae to it are 
by no means completely understood. While the facts of zonal 
distribution of the red, brown, and green forms support in a general 
way the well-known Oerstedt-Engelmann theory, yet the corres¬ 
pondence is by no means so complete as to satisfy us completely. 
Oltmanas’ own observations, and Berthold’s also, seem to shew' 
that in many cases the Florideae behave rather as shade plants than 
as green-light plants, ix., they live in weak white light rather than 
in spectrally selected light. In spite of Gaidukov’s striking obser¬ 
vations' on complementary chromatic adaptation in Oscillaria, the 
variations in the pigment of various Florideae are not easily 
explained on his principles. Much more experiment, as well as 
observation in “freie Natur,” is required before these problems can 
reach anything like a definitive solution. Meanwhile it is, we think, 
impossible to doubt that the “complementary” principle must play 
an important, perhaps the leading, part in colour determination. 
Professor Oltmanns has some interesting remarks on methods 
of protection against over-illumination. It appears that Fuchs, 
Codium and the Rhodomeleae tend to cover themselves with hairs 
when exposed to strong light. These colourless hairs, so widely 
spread among marine algae, have often been considered as respiratory. 
They may also, Professor Oltmanns thinks, be of use because they 
increase the food-absorbing surface. The iridescent colours of many 
red seaweeds are due to reflecting masses or layers of substance 
immediately below the external cell wall, and these probably serve 
to decrease the amount of light reaching the chromatophores. 
In the chapter on Periods of Vegetation it is shewn that in 
temperate regions the great vegetative period is the spring, and this 
applies in a general way to marine and freshwater forms, to Benthos 
and Plankton alike. The summer flora of the more northern seas 
may be regarded as a continuation of the spring vegetation, owing 
1 See “Chromatic Adaptation,” Nbw Piiytologist, Vol. III., p.237. 
